1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly to a liquid crystal display device in which a pair of transparent substrates are opposed to one another via a plurality of columnar spacers.
2. Description of Related Art
LCD devices have advantages of a smaller thickness, lower power dissipation and a lower weight, and thus is increasingly used as flat-panel display devices. FIG. 9 shows a sectional view of a part of a conventional liquid crystal panel which configures an LCD device together with drive circuits etc. The liquid crystal panel 200 has a liquid crystal layer 202 sandwiched between a pair of transparent substrates 201 and 203. Generally, one of the pair of transparent substrates, for example, transparent substrate 201, is constructed as an array substrate having an array of switching elements, and the other, transparent substrate 203, is constructed as a counter substrate in which color filters, etc., are formed.
The array substrate 201 is designed based on the mode of driving the liquid crystal. For example, in an IPS (in-plane-switching) mode LCD device, a structure having an organic insulator film 205 provided between an interconnection layer and an electrode layer is adopted responding to the demand for increasing an aperture ratio of pixels. The term “aperture ratio” used herein is a ratio of an effective light-transmitting area in each pixel to the total pixel area thereof.
In an LCD device of a reflecting type, for example, in order to form unevenness on a reflecting film thereof, a structure is also provided in which the organic insulator film 205 is provided on the array substrate 201. In the liquid crystal panel 200, the array substrate 201 and the counter substrate 203 are opposed to each other with a predetermined cell gap therebetween defined by columnar spacers 204 each having a specific degree of elasticity, whereby the cell gap is maintained uniformly and accurately with the display area of the display panel.
FIG. 10 shows a top plan view of the liquid crystal panel 200. If the columnar spacers 204 are disposed for all the pixels in the liquid crystal panel 200, an accurate alignment is difficult to achieve in the operation for assembly of the array substrate 201 and the counter substrate 203, due to the excessive number of columnar spacers 204. In addition, the liquid crystal panel 200 may have an ununiform cell gap, after liquid crystal is injected between the pair of substrates 201 and 203. This is because the excessive number of columnar spacers makes it difficult to crush the columnar spacers between the substrates 201 and 203, although all the columnar spacers 204 should be crushed uniformly between the substrates. In order to avoid this problem in the liquid crystal panel 200, the columnar spacers 204 are disposed each for several pixels, as shown in FIG. 10.
Generally, in the liquid crystal panel 200, it is desired that the cell gap be formed smaller in order to accelerate the response speed upon the image display of the liquid crystal panel 200. However, in the liquid crystal panel 200, as the cell gap is narrowed, the height H1 of the columnar spacer 204 must be lower, whereby the amount of possible elastic deformation of each columnar spacer 204 is reduced, and hence gap unevenness occurs. Further, since the accuracy of the cell gap is mainly determined based on the accuracy of the height H1 of the columnar spacer 204 and the accuracy of the thickness of the organic layer 205, the error between a designed value of the cell gap and an actual cell gap is increased with the increase of these unevenness factors.
There is a technology described in Japanese Patent Laid-Open Publication No. 2003-121859 as a technique for solving the above-described problems. FIG. 11 shows a sectional view of the LCD device described in the patent publication. In this technology, the organic insulator layer 205 is removed at positions corresponding to the positions for forming the columnar spacers 204, and spacer holes 206 each for receiving the columnar spacer 204 are formed. The height H2 of each columnar spacer 204 is increased as compared with the cell gap, as a result of which the amount of elastic deformation of the columnar spacer 204 can be increased. This allows the LCD device to have a more uniform cell gap. In addition, since the accuracy of the cell gap is determined based on the accuracy of the height of the columnar spacer 204, the error between the designed value of the cell gap and the actual cell gap is reduced with the smaller unevenness factor.
It is to be noted that another organic film is formed as an alignment film on each of the array substrate 201 and the counter substrate 203. The alignment film is, as shown in FIG. 12, rubbed by a rubbing roller 207 which rotates at a high speed. In the rubbing treatment, the surface of the alignment film is rubbed to generate dust or fine particles of the alignment film. This dust is generally pushed toward the rear side of the rubbing roller 207 in the rubbing direction. The spacer holes 206 formed in the organic insulator film 205 for the columnar spacers may receive therein the dust of the alignment film.
FIG. 13 shows an enlarged view in the vicinity of one of the columnar spacers 204 in the liquid crystal panel 200a. In the assembled state of the liquid crystal panel 200a, the dust of the alignment film remains in the vicinity of the contact surface between the columnar spacer 204 and the array substrate 201a. If an external force is applied to the liquid crystal panel 200a in this state, the dust of the alignment film may exit the spacer hole 206 due to the impact of the external force so that the dust of the alignment film is scattered into the liquid crystal layer 202. The dust of the alignment film 208 thus scattered in the liquid crystal layer 202 disturbs, as shown in FIG. 14, the direction of the liquid crystal molecules aligned by the alignment film, thereby causing a malfunction in the image display of the liquid crystal panel 100a. 